A transparent dome cover is widely applied to the field of optical imaging, mainly provides mechanical protection for a camera and a lens, and has excellent optical properties, so as to minimize the adverse effects of imaging. A transparent cover for the field of security and protection is made from high-performance optical plastics usually. In order to utilize an internal space to the greatest extent, some transparent dome covers will be made in a super-hemispherical shape.
The dome camera is manufactured by using an injection process usually. In order to ensure the de-molding performance, the dome camera cannot be made to be completely spherical surface. Usually, a central area of the dome camera is processed to be spherical surface, and an edge area is processed to be conical surface. In the central area of the dome cover, in order to ensure a better optical property, both an internal surface and an external surface are concentric spherical surfaces. In the edge area of the dome cover, both an internal surface and an external surface are conical surfaces. The conical surface and spherical surface parts are connected tangentially, and the thickness remains uniform, so the characteristics of simple processing and good image quality of a central part are provided.
The inherent defects of the dome cover are that focal power in a meridian direction and a sagittal direction is different accordingly due to different curvatures of a conical surface in the two directions. After light beams pass through the dome cover, light beams in the meridian direction and the sagittal direction thereof cannot be focused on the same point, thereby making imaging fuzzy, generating remarkable astigmatism, and influencing the imaging effect. An optical system having a large focal length and a large caliber particularly has the severe defects. Due to the defect of astigmatism, an application occasion of the dome camera is greatly limited.
Another technology is that a concentric spherical surface type dome camera is manufactured by using a blow molding process. The concentric spherical surface type dome camera has consistent focal power. Due to the same curvature radius of the meridian direction and the sagittal direction, the astigmatism is avoided, and meanwhile, the problem of de-molding does not exist. However, under the limitation of characteristics of the blow molding process, the wall thickness uniformity of the dome cover is bad, the imaging quality is bad, and requirements of a high-definition imaging optical system cannot be met.
Therefore, a technical solution is expected to overcome or at least reduce one or more of the aforementioned defects of the conventional art.